In certain electronic circuits, a voltage reference generator is used in the production of a voltage. In one example, a DC-to-DC voltage converter will generally include a reference load that is utilized in the generation of a reference voltage. In circuits in which power consumption is critical, the design of a reference load can have a significant impact on system performance. The reference load may be utilized to adjust the reference voltage as needed, which will affect how well the reference voltage potential can be maintained and adjusted. In addition, the reference load itself will consume a certain amount of power, which adds to the total power consumption of the system.
In one example, when a PC (personal computer) system is powered down, a RTC (real time clock) circuit may derive power from another power source, such as a self-contained source in the PC. A 3.0-volt coin cell lithium battery is generally used because such batteries are widely available and very inexpensive. In certain systems, another power source, such as a charged capacitor, may provide the power for the RTC circuit when the system is powered down. A PC system may be turned off for long periods of time, possibly for years, depending upon usage and the length of time a system may stay in storage. Therefore, an RTC circuit may potentially need to derive power from a coin cell battery or other such power source for a period of years to maintain system time.
As computer processes move towards lower voltages in order to reduce power consumption and to increase speed in digital sections, the voltage of a coin cell battery may need to be stepped down to a lower voltage, such as a voltage range of less than 2 volts, depending upon the process voltage. A system may include a DC-to-DC converter using a reference load to generate a reference voltage.
FIG. 1 illustrates one example of a conventional reference load incorporated in a DC-to-DC voltage generator. A voltage supply 105, such as a coin battery, provides a voltage to the circuit. The voltage supply is connected to the source of output transistor 135. The converter circuit includes diode-connected transistors Q2 110 and Q3 115, which provide voltage drops and step down the voltage to the gate of output device 135. A reference load is provided, shown in FIG. 1 as comprising diode-connected transistors Q4 120 and Q5 125. Connected between Q4 120 and Q5 125 is transistor device Q1 130. A current through Q1 130 to adjust the reference load is provided by a clamping control circuit 160, which is controlled by a signal 165. The output voltage 140 from the circuit is supplied to certain devices, shown as an RTC oscillator 145 and RTC logic 150 utilized in maintenance of system time.